1. Field of the Invention
The present invention relates to a method and apparatus best-suited to make dental root canal filling points, which are formed of a thermoplastic material in the form of an elongated cone and which are used as a filling and obturating material or sealing material for pulp cavities formed after pulpectomy or the disinfection of infected root canals during dental treatments, inter alia, to make a dental root canal filling point referred usually to as a gutta-percha point, and an apparatus for making the same.
2. Statement of the Prior Art
Conventional dental root canal filling points usually called the gutta-percha points in the form of an elongated cone have been fabricated by cutting into a wedgy shape a thin, elongated and complanate material comprising a composition usually containing 60 to 70% of zinc oxide, 20 to 25% of refined gutta-percha, a heavy metal salt for improving radio-opacity and a small amount of wax, resin and the like, then heating and softening the material at about 80.degree. C. and finally shaping the softened material into an elongated cone, while manually rolling it on a kneading plate with the use of a spatula.
By reason that the conventionally used gutta-percha points are prescribed in size and shape according to the standards of dental root canal instruments used for the preparation of root canals, however, the number of their types reach as many as 19 in terms of sizes of the international standards in particular, while severer dimensional tolerances of as small as .+-.0.04 mm is required for their diameters. Moreover, numerous types of products varying in diameter from a lowest 0.1 mm to a highest 1.5 mm in the length range of 10 to 35 mm are commercially available because various dental-root-canal-filling-point makers make nonstandardized products of their own in addition to the standardized ones. In order to make dental root canal filling points, the only option has been rely upon skilled workers. This has implied that it is necessary to train unskilled workers, and has posed a problem that it is difficult to meet an increased demand in the recent advancement of dental treatments.
In order to simplify the production of dental root canal filling points and increase the yield of products by mechanical means, molding processes with extruders and casting dies have been attempted. However, owing to much severer accuracies imposed upon the dimensions and shapes of the dental root canal filling points, as mentioned above, a cost problem arises with possible burring or failure of the products during the releasing of the product from the molds. As yet, there has been thus unavailable any method capable of mechanically mass-producing the dental root canal filling points. In consequence, the production of the dental root canal filling points is still carried out by man power. In that case, the efficiency of inspection of the products is very low, since all the products should individually be inspected after they have been broken down into as many standards as mentioned above. Worse yet, barely about 65% of the products are accepted due to a high probability of some products being misclassified and rejected even by those versed in the art, resulting in waste in the production, such has been the problems difficult to solve in the prior art.
Therefore, the present inventors have made intensive and extensive studies of how to carry out in a mechanical, simple and dimension-stable manner the production of the dental root canal filling points, which have been considered difficult to make by other means than manual ones and, as a result, have found out that the method to be described below enables them to be fabricated both efficiently and mechanically.